This invention relates to the manufacturer of printheads used in inkjet printers, and more specifically to an inkjet printhead used in an inkjet print cartridge having improved dimensional control and improved step coverage.
One type of inkjet printing system uses a piezoelectric transducer to produce a pressure pulse that expels a droplet of ink from a nozzle. A second type of inkjet printing system uses thermal energy to produce a vapor bubble in an ink-filled chamber that expels a droplet of ink. The second type is referred to as thermal inkjet or bubble jet printing systems.
Conventional thermal inkjet printers include a print cartridge in which small droplets of ink are formed and ejected towards a printing medium. Such print cartridges include inkjet printheads with orifice plates having very small nozzles through which the ink droplets are ejected. Adjacent to the nozzles inside the inkjet printhead are ink chambers, where ink is stored prior to ejection. Ink is delivered to the ink chambers through ink channels that are in fluid communication with an ink supply. The ink supply may be, for example, contained in a reservoir part of the print cartridge.
Ejection of an ink droplet through a nozzle may be accomplished by quickly heating a volume of ink within the adjacent ink chamber. The rapid expansion of ink vapor forces a drop of ink through the nozzle. This process is commonly known as xe2x80x9cfiring.xe2x80x9d The ink in the chamber may be heated with a transducer, such as a resistor, that is aligned adjacent to the nozzle.
In conventional thermal inkjet printhead devices, thin film resistors are used as heating elements. In such thin film devices, the resistive heating material is typically deposited on a thermally and electrically insulating substrate. A conductive layer is then deposited over the resistive material. The individual heater element (i.e., resistor) is dimensionally defined by conductive trace patterns that are lithographically formed through numerous steps including conventionally masking, ultraviolet exposure, and etching techniques on the conductive and resistive layers. More specifically, the critical width dimension of an individual resistor is controlled by a dry etch process. For example, a reactive ion etch process is used to etch portions of the conductive layer not protected by a photoresist mask. The conductive layer is removed and a portion of the resistive layer is exposed. The resistive width is defined as the width of the exposed resistive layer between the vertical walls of the conductive layer. Conversely, the critical length dimension of an individual resistor is controlled by a subsequent wet etch process. A wet etch process is used to produce a resistor having sloped walls defining the resistor length. Sloped walls of a resistor permit step coverage of later fabricated layers.
As discussed above, conventional thermal inkjet printhead devices require both dry etch and wet etch processes. The dry etch process determines the width dimension of an individual resistor, while the wet etch process defines both the length dimension and the necessary sloped walls of the individual resistor. As is well known in the art, each process requires numerous steps, thereby increasing both the time to manufacture a printhead device and the cost of manufacturing a printhead device.
One or more passivation and cavitation layers are fabricated over the conductive and resistive layers and then selectively removed to create a via for electrical connection of a second conductive layer to the conductive traces. The second conductive layer is pattered to define a discrete conductive path from each trace to an exposed bonding pad remote from the resistor. The bonding pad facilitates connection with electrical contacts on the print cartridge. Activation signals are provided from the printer to the resistor via the electrical contacts.
The printhead substructure is overlaid with an ink barrier layer. The ink barrier layer is etched to define the shape of the desired firing chamber within the ink barrier layer. The firing chamber is situated above, and aligned with, the resistor. The ink barrier layer includes a nozzle print cartridge adjacent to each firing chamber.
In direct drive thermal inkjet printer designs, the thin film device is selectively driven by the above-described thermal electric integrated circuit part of the printhead substructure. The integrated circuit conducts electrical signals directly from the printer microprocessor to the resistor via the two conductive layers. The resistor increases in temperature and creates super-heated ink bubbles for ejection from the chamber through the nozzle. However, conventional thermal inkjet printhead devices suffer from inconsistent and unreliable ink drop sizes and inconsistent turn on energy required to fire an ink droplet.
It is desirous to fabricate an inkjet printhead capable of producing ink droplets having consistent and reliable ink drop sizes. In addition, it is desirous to fabricate an inkjet printhead having a consistent low turn on energy (TOE) required to fire an ink droplet, thereby providing greater control of the size of the ink drops.
One aspect of the present invention provides a fluid ejection apparatus, such as a printhead, including an insulative dielectric and first and second conductors disposed on the insulative dielectric. A space is formed between the first and second conductors. A dielectric material is fabricated on top of the first and second conductors and in the space. A first via is formed in the dielectric material adjacent the first conductor. A second via is formed in the dielectric material adjacent the second conductor. A resistive material layer is fabricated on top of the dielectric material. A first electrical connection to the resistive material layer is formed with the first conductor in the first via. A second electrical connection to the resistive material layer is formed with the second conductor in the second via.